1. Field of the Invention
This invention relates to an apparatus for manufacturing an electron source and an image forming apparatus.
2. Related Background Art
There have been known two types of electron-emitting device; the thermoelectron emission type and the cold cathode electron emission type. Of these, the cold cathode emission type refers to devices including field emission type (hereinafter referred to as the FE type) devices, metal/insulation layer/metal type (hereinafter referred to as the MIN type) electron-emitting devices and surface conduction electron-emitting devices. Examples of FE type device include those proposed by W. P. Dyke & W. W. Dolan, "Field emission", Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, "PHYSICAL Properties of thin-film field emission cathodes with molybdenum cones", J. Appl. Phys., 47, 5284 (1976).
Examples of MIN device are disclosed in papers including C. A. Mead, "The tunnel-emission amplifier", J. Appl. Phys., 32, 646 (1961).
Examples of surface conduction electron-emitting device include one proposed by M. I. Elinson, Radio Eng. Electron Phys., 10 (1965).
A surface conduction electron-emitting device is realized by utilizing the phenomenon that electrons are emitted out of a small thin film formed on a substrate when an electric current is forced to flow in parallel with the film surface. While Elinson proposes the use of SnO.sub.2 thin film for a device of this type, the use of Au thin film is proposed in [G. Dittmer: "Thin Solid Films", 9, 317 (1972)] whereas the use of In.sub.2 O.sub.3 /SnO.sub.2 and that of carbon thin film are discussed respectively in [M. Hartwell and C. G. Fonstad: "IEEE Trans. ED Conf.", 519 (1975)] and [H. Araki et al.: "Vacuum", Vol. 26, No. 1, p. 22 (1983)].
FIG. 34 of the accompanying drawings schematically illustrates a typical surface conduction electron-emitting device proposed by M. Hartwell. In FIG. 26, reference numeral 1 denotes a substrate. Reference numeral 4 denotes an electroconductive thin film normally prepared by producing an H-shaped thin metal oxide film by means of sputtering, part of which eventually makes an electron-emitting region 5 when it is subjected to an electrically energizing process referred to as "energization forming" as described hereinafter. In FIG. 26, the thin horizontal area of the metal oxide film separating a pair of device electrodes has a length L of 0.5 to 1 [mm] and a width W of 0.1 [mm].
It should be noted, however, that a surface conduction electron-emitting device does not necessarily have a H-shaped film prepared in a single operation. Alternatively, a pair of electrodes may be arranged in parallel with each other like the pillars of H in the first place and thereafter an electroconductive thin film may be formed to link the electrodes. The material and the thickness of the thin film may be different from those of the electrodes.
Conventionally, an electron emitting region 5 is produced in a surface conduction electron-emitting device by subjecting the electroconductive thin film 4 of the device to an electrically energizing preliminary process, which is referred to as "energization forming". In the energization forming process, a constant DC voltage or a slowly rising DC voltage that rises typically at a rate of 1 V/min. is applied to given opposite ends of the electroconductive thin film 4 to partly destroy, deform or transform the film and produce an electron-emitting region 5 which is electrically highly resistive. Thus, the electron-emitting region 5 is part of the electroconductive thin film 4 that typically contains a gap or gaps therein so that electrons may be emitted from the gap. Note that, once subjected to an energization forming process, a surface conduction electron-emitting device comes to emit electrons from its electron emitting region 5 whenever an appropriate voltage is applied to the electroconductive thin film 4 to make an electric current run through the device.
Since a surface conduction electron-emitting device has a particularly simple structure and can be manufactured in a simple manner, a large number of such devices can advantageously be arranged on a large area without difficulty. As a matter of fact, a number of studies have been made to fully exploit this advantage of surface conduction electron-emitting devices. For example, there have been proposed various types of image forming apparatus including a self-emission type flat image forming apparatus.
In a typical example of electron source comprising a large number of surface conduction electron-emitting devices, the devices may be arranged in parallel rows and the positive and negative electrodes of the devices of each row may be connected to respective common wirings (ladder arrangement) as shown in FIG. 14 or a matrix of wirings may be formed and the devices may be connected to the respective wirings as shown in FIG. 10.
In order for an image forming apparatus comprising a number of electron-emitting devices to stably provide clear and bright images, the devices are required to operate uniformly and efficiently for electron emission. The efficiency of a surface conduction electron-emitting device is defined by the ratio of the electric current flowing between the paired electrodes of the device (hereinafter referred to "device current") to the electric current produced by electrons emitted into the vacuum of the image forming apparatus (hereinafter referred to as "electron emission current") when a certain voltage is applied to the device electrodes. If all the electron-emitting devices of the electron source operate uniformly and efficiently for electron emission in, for instance, an image forming apparatus comprising a fluorescent body as its image forming member, such an apparatus can make a high definition image forming apparatus or television set that can be very flat and consumes power only at a reduced rate. By turn, the drive circuit and other components of such an energy saving apparatus may be manufactured at low cost.